There is a growing interest in energy storage technologies as technology development and demand with respect to mobile phones, camcorders, notebook PCs, and even electric vehicles have recently increased.
In particular, among the energy storage technologies, there emerges an interest in lithium secondary batteries having high energy density and high voltage and capable of being charged and discharged.
The lithium secondary battery is generally composed of a positive electrode and a negative electrode, which include electrode active materials capable of intercalating/deintercalating lithium ions, and an electrolyte as a lithium ion transfer medium.
As the electrolyte, a liquid electrolyte including a non-aqueous organic solvent, in which an electrolyte salt is dissolved, or a gel polymer electrolyte further including a matrix polymer with the liquid electrolyte is being used.
Gas may be generated in the secondary battery due to the decomposition of the electrolyte during charge and discharge of the lithium secondary battery or a side reaction between the electrode and the electrolyte, and the gas generation is further increased during high-temperature storage.
The continuously generated gas may not only cause an increase in internal pressure of the battery to cause deformation of the battery, for example, thickness expansion of the battery, but may also locally change adhesion on an electrode surface in the battery to prevent an electrode reaction from occurring equally on the entire electrode surface.
Thus, in order to improve stability and high output characteristics of the battery, there is a need to develop a lithium secondary battery in which stability is improved by suppressing gas generation and exothermic reaction during high-temperature storage and overcharge.